Retrievable well packer apparatus



April 21, 1910 D. E. YOUNG 3,507,326

RETRIEVABLE WELL PACKER APPARATUS Filed Aug. 30, 1968 3 Sheets-Sheet 2 3 45 52 5/ 53 .95 (Z /flfl 4/ l N V 151V] UR.

ATTORNEY 3,507,326 RETRIEVABLE WELL PACKER APPARATUS David E. Young, Bellaire, Tex., assignor to Schlumberger Technology Corporation, New York, N.Y., a corporation of Texas Filed Aug. 30, 1968, Ser. No. 756,442 Int. Cl. E21b 23/06 US. Cl. 166-120 Claims ABSTRACT OF THE DISCLOSURE The particular embodiment disclosed herein as illustrative of one form of the present invention in well packers comprises a body member and packing means for packing off a well bore, expander means and normally retracted slip means shiftable by said expander means into anchoring positions against a well conduit wall, an upwardly facing surface on said expander means subject to fluid pressure in the well bore below said packing means, an enclosed chamber defined in part by a downwardly facing surface on said expander means, and hydraulic means responsive to greater fluid pressure below said packing means for reducing the pressure in said chamber.

This invention relates generally to well tools used for packing off or isolating well bore zones, and more specifically to a retrievable well packer having expansible anchors and packing for preventing fluid movement in either direction past its sealing point.

To conduct testing, remedial, stimulation or production operations in a particular zone in a well, the zone can be isolated by well tools which can be positioned in the well bore below and above the zone. The lower tool, commonly called a bridge plug, functions to seal off the entire cross-section of the well bore to isolate the zone from fluids at their hydrostatic pressures which are below the zone. The upper tool, commonly called a packer, is generally retrievable and functions to seal off the annulus between a tubing string attached to the packer and the well casing to isolate the zone from fluids at their hydrostatic pressures which are above the zone. The tubing string provides a means of access to the isolated zone for fluid flow, testing tools, or other instruments which can be lowered therethrough. Although permanent type bridge plugs have been used for the lower tool, it has become common practice to use retrievable type bridge plugs which can be left in the well bore if desired, but which can also be retrieved to the surface for further and repeated usage if desired.

Inasmuch as fluid pressure may be imposed on a bridge plug either from above or below, it is necessary to anchor the plug against movement in both directions. In the past, such anchoring has been accomplished for the most part by independently operable slips and expanders, one slip and expander combination being arranged to prevent movement in one direction and the other slip and expander combination coming into play to prevent movement in the other direction. A more recent advance in the art, shown in the 1968-69 Composite Catalog of Oil Field Equipment and Services, page 2755, enables only a single slip and expander combination to prevent movement in both directions, This slip and expander combination is mechanically set against movement in a downward direction, and a hydraulic system including a piston on the expander which is responsive to greater fluid pressure below the plug functions to hold the slips in set position, thereby preventing upward movement.

In the above-mentioned type of bridge plug, it is deh States Patent Office 3,507,326 Patented Apr. 21, 1970 is for the reason that during pressuring operations such as fracturing, the fluids in the well bore may contain sand or other foreign matter which tends to settle out on top of the plug. If the hydraulic system is exposed to such fluids and foreign matter, then of course these substances may enter the system and cause damage to seals and seal surfaces, or may plug ports or the like and prevent satisfactory operation of the hydraulic system. This adds to the maintenance required to ensure that the plug parts are in satisfactory working condition for repeated usage.

It is accordingly a broader object of the present invention to provide a new and improved well packer or plug having a single set of slips and an expander for preventing movement in either direction, and including a hydraulic system which is closed when the tool is set and functions to hold the slips against upward movement due to pressure imposed on the tool from below. Thus the operation of hydraulic system is not adversely affected by the presence .of foreign substances in the well bore above the tool, thereby increasing the releasability of the tool and reducing maintenance problems.

This and other objects of the present invention are attained by an apparatus, illustrated in a retrievable bridge plug form, which includes a packing element for packing off the well bore, and a single slip and expander combination for preventing movement in either direction in the well bore. The expander is provided with upper and lower transverse surfaces, the upper surface being subject to fluid pressure in the well bore below the packing elements. A variable volume chamber is formed in part by the lower surface on the expander and is enclosed when the plug is set. Hydraulic means responsive to greater fluid pressure in the well bore below the packing elements is effective to increase the volume of the enclosed chamber in order to reduce the fluid pressure acting on the lower expander surface, thereby developing pressure differential across to the piston. The pressure differential is effective as downward force on the expander, thus providing an anchoring force on the slips to prevent upward movement of the plug.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with other objects and advantages thereof, may be best understood by way of example of one embodiment thereof when taken in conjunction with the following drawings in which:

FIGURE 1 is a schematic view of a well having well tools positioned therein for isolating a zone in which operations are to be performed;

FIGURE 2A is a sectional view of the upper portion of an apparatus in accordance with the present invention with parts in relative positions for longitudinal movement in a well conduit;

FIGURE 2B is a view similar to FIGURE 2A showing the lower portion of the apparatus of the present invention and forms a lower continuation of FIGURE 2A;

FIGURE 3 is a developed plan view showing schematically the lug and channel arrangement of the mandrel control section;

FIGURE 4A is a sectional view similar to FIGURE 2A but with parts in their relative positions when the apparatus is set in a well conduit;

FIGURE 4B is the lower continuation of FIGURE 4A; and

FIGURE 5 is an enlarged sectional view of a portion of the hydraulic system of the present invention.

In order to conduct remedial, stimulation or production operations in a cased well bore which traverses a formation, it may be necessary to isolate a zone of the well bore adjacent the formation. This can be accomplished by lowering upper and lower packers, such as P-1 and P-Z connected together by a running tool R as shown in FIGURE 1, on a pipe string T into the well bore. The lower packer P-2 is set to plug the well bore at the lower end of the zinc Z. The running tool R is released from the lower packer P-2, and the upper packer P-l is elevated and then set at the upper end of the zone. The pipe string T provides a passageway from the earths surface through the upper packer and into the zone Z for fluid flow as well as various wireline or other tools. When the operation is completed, the upper packer P-l can be released and reconnected to the lower packer, P-2 which is then released so that both packers can be withdrawn from the well or moved to another location in the Well bore. The upper packer can be constructed according to teachings of McGill, Patent No. 3,399,729, dated Sept. 3, 1968.

Referring now to FIGURES 2A and 2B for details of the lower packer, commonly called a retrievable bridge plug, apparatus in accordance with the present invention includes a generally tubular body member extending throughout the length of the tool. The body member 10 has a central bore 11 which is open at its lower end by several side ports 12. The upper end of the body member 10 is closed by a threadedly attached connector head 13 having J-slots 14 or the like in its outer periphery for connecting to a conventional running and retrieving tool R.

A plurality of bypass ports 15 extend laterally through the wall of the body member 10 below the connector head 13. Sealing elements 16 and 17 are received in annular grooves above and below the ports 15. A sleeve valve 18 is slidably disposed on the body member 10 adjacent the ports 15 and is movable between a lower position as shown in FIGURE 2A where the bypass ports 15 are open, and an upper position Where the upper end 7 of the sleeve valve 18 abuts the lower end of the connector head 13. In the upper position, the sleeve valve 18 spans the ports 15 and, in combination with the sealing elements 16 and 17, functions to block fluid flow therethrough. A plurality of spring fingers 19 extend from the lower end of the sleeve valve 18 and have enlarged head portions 20 which are sized to engage an annular shoulder 21 formed on the body member to releasably hold the valve sleeve in either open or closed position.

The body member 10 may be considered as being constituted by an upper section 25 and a lower section 26 which are coupled together by a control mechanism 27. The upper section has a depending sleeve 28 with an internal recess 29 and a lower reduced portion 30. The lower body section 26 has a sub 31 extending into the sleeve 28, the sub being provided with diametrically opposed lugs 32 which are cooperable with a slot configuration 33 formed on the recess 29. Thus the body sections 25 and 26 can be manipulated to move one relative to the other to a limited extent both longitudinally and rotationally for purposes which will be more fully described hereafter. Seal element 34 between the lower portion and the sub 31 are provided to prevent fluid leakage.

The lower body section carries a generally tubular compression sleeve 36 which has a downwardly facing shoulder or abutment 37. The abutment 37 engages the upper end of a packing structure 38 which can be formed by a plurality of elastomeric rings 39 which are adapted, when compressed, to be expanded into sealing contact with the well bore wall in a typical manner. A suitable bearing 40 is mounted between an upwardly facing shoulder 41 on the compression sleeve 36 and a downwardly facing shoulder 42 on the body section 26 to reduce frictional resistance to rotation of the body section within the compression sleeve under loaded conditions. Coupled to the upper end of the compression sleeve 36 is a sleeve extension 45 having an inwardly extending shoulder 46 carrying a seal ring 47. The upper end of the reduced section 30 is recessed somewhat so that when the parts are in the relative positions shown in FIGURE 2A, there is a flow passage provided between the seal ring 47 and the section 30. The upper end portion of the sleeve extension 45 is notched or otherwise ported at 48 to communicate with the well annulus. The inner respective wall surfaces 50 and 51 of the compression sleeve 36 and its extension 45 are spaced laterally away from the body section 26 to provide a chamber space 52. The chamber space 52 is continued past the bearing 40 by one or more radially cut and vertically disposed grooves 53. When the parts are in the relative positions shown in FIGURE 2A, the runningin positions, the chamber space 52 is in communication with the well annulus above the packing structure 38 and will reflect whatever hydrostatic fluid pressure which may be present in the annulus. However, when the upper body section 25 is moved upwardly relative to the lower body section 26, the seal ring 47 on the extension 45 is arranged to engage a seal surface 54 on the reduced section 30 in order to close the chamber space 52 from communication with the well bore.

The slot configuration 33, shown in developed view in FIGURE 3, is arranged to cooperate with lugs 32 in a manner to couple the body sections 25 and 26 in a contracted relative position, where the chamber 52 is open to the well bore, and in an extended position where the chamber is closed and cannot be opened to the well bore except by appropriate manipulation of the upper section 25. When the parts are in relative positions for running into a well bore, the lugs 32 occupy positions 1 between upwardly and downwardly facing shoulders 55 and 56 on the sleeve 27 which can engage the lugs to prevent sufficient relative movement of the sections 25; and 26 to enable the seal ring 47 to engage the seal surface 54. Therefore, the chamber 52 will remain in communication with the well bore while the plug is being lowered into the well bore. However, by torquing the upper body section 25 to the right relative to the lower body section 26, and then lifting the upper body section, the lugs 32 can move first to positions 2 and then into vertical portions 57 of the slot configuration 33, whereupon the seal surface 54 can be engaged with the seal ring 47 to close the chamber 52. The lugs 32 can be moved against the side walls 58 of the slots at positions 3 and underneath downwardly facing shoulders 59 on the sleeve 28, which shoulders are spaced downwardly relative to the upper sleeve shoulder 56 so that the upper body section 25 cannot be lowered sufficiently at positions 3 of the lugs to disengage the seal surface 54 from the seal ring 47. Therefore, when the lugs 32 are in the reccessed portion 60 of the slots, the chamber 52 will remain closed unless and until the body section 25 is torqued to the left and then lowered to enable the lugs to move between the sleeve shoulders 56 and 5,7 and reoccupy the positions 1.

An expander assembly 62 (FIGURE 2B) is mounted on the lower body section 26 below the packing structure 38 and includes an expander cone 63 having outer surfaces 64 inclining downwardly and inwardly toward the body section. A sleeve 65 couples the expander cone 63 to a piston member 66 having its inner periphery sealingly slidable on the compression sleeve 36. An annular floating piston member 67 is movable between the body section 26 and the expander sleeve 65 and is biased upwardly against a stop shoulder 68 by a coil spring 69 or the like which rests on the expander cone 63. The piston member 66 has a lower face 70 which forms a wall of the chamber space 52 which extends between the body section 26 and the compression sleeve 36 to a location between the piston members 66 and 67. Appropriate O-rings or other seals 71-74 which seal between the pistons and adjacent wall surfaces are provided to prevent fluid leakage from the chamber space.

The piston member 66 can be formed to extend up wardly toward the packing structure 38 and is provided with an inwardly extending flange 75 engaging above splines 76 on the lower end portion of the compression sleeve 36. Such engagement limits downward movement of the expander assembly 62 relative to the body section 26, and the splines 76 engage complementary splines 77 to prevent relative rotation between the body section and the expander assembly. The flange 75 supports a gauge ring 78 which provides an upwardly facing abutment engaging the lower end of the packing structure 38.

A cage member 80 is movably mounted on the lower end portion of the body section 26 above a stop flange 81. The cage member 80 has radially directed recesses receiving circumferentially spaced drag blocks 82 which are urged outwardly by coil spring 83 into frictional contact with the well casing. A plurality of wickered slip elements 84 can be pivotally coupled to the upper end of the cage member 80 by reins 85 or the like, and are arranged for lateral movement between retracted and expanded positions. The slip elements 84 have inner inclined surfaces 86 which slidably engage the outer inclined surfaces 65 on the expander cone 63, and the slip elements can be slidably coupled to the expander cone by a conventional dovetail tongue and groove connections 87.

A clutch assembly 90 is provided for controlling relative longitudinal movement between the cage member 80 and the body section 26. The clutch assembly 90 includes a segmental clutch nut 91 which is received within an internal annular recess 92 in the cage member, each of the nut segments being secured against rotation relative to the cage member by lugs 93 which engage in peripheral slots in the segments. Upper and lower band springs 94 and 95 permit lateral movement of the nut segments while continuously urging the segments toward contracted positions around the body section 26. Each nut segment can have upper left-hand threads 96 and lower right-hand threads 97 which are cooperable with threads companion 98 and 99 on the body section 26 to secure the body section relative to the cage member in spaced longitudinal positions. An inwardly biased stop lug 100 can initially enage within a shouldered recess 101 in the mandrel to prevent counter-clockwise rotation of the cage member 80 relative to the mandrel during lowering, thereby preventing rotational locking of the lower end surface of the cage member against the upper face of the gauge stop ring 81.

In operation, the parts can be assembled as shown in FIGURES 2A and 2B and lowered in the well casing to a location where it is desired to form a pressure bridge, for example, at the lower end of a zone as shown in FIGURE 1. During lowering, the tubing string T is connected to the connector head 13 by the running tool R, and the sleeve valve 18 is in its lower position where the bypass ports are open. Thus, fluids in the well bore can bypass through the tool via the lower ports 12, the body bore 11 and the bypass ports 15, as well as around the packing structure 38 to provide ample bypass area. During lowering, the lower thread 97 of the segmented clutch nut 91 are in engagement with the lower body threads 99 to prevent upward movement of the cage member 80 relative to the body member 10. The slip segments 84 are thus held in retracted positions and cannot move upwardly to be shifted outwardly by the expander cone 63. The packing structure 38 is, of course, retracted, and the lugs 32 on the sub 31 are in the posi tions 1 between the sleeve shoulders 55 and 56 so that the chamber space 52 is vented to the well bore.

At setting depth, the tool is halted and the body membar is torqued or turned several turns to the right by rotation of the tubing string T. Inasmuch as the cage member 80 will not rotate due to frictional engagement of the drag blocks 82 with the casing, rotation of the body section 26 will release the clutch nut threads 97 from 6 the body threads 99 to enable downward movement of the body member 10. During such rotation the control lugs 32 will move to the positions 2 within the slot configuration 33. Downward movement of the body member 10 by lowering the pipe string T will cause the compression sleeve 36, the packing structure 38 and the expander assembly 62 to move downwardly, thereby bringing the expander cone 63 behind the slip segments 84 and shifting the slip segments into gripping engagement with the well casing Wall as shown in FIGURE 4B. The drag blocks 82 support the cage member and the slips 84 against downward movement.

When the slip teeth 102 are firmly engaged, the expander assemly 62 is supported against further downward movement, thereby preventing further downward movement of the lower gauge ring or abutment 78. Accordingly, the weight of the tubing string T can be imposed on the body member 10, causing downward movement of the compression sleeve 36 and compression of the packing structure 38 between the upper abutment 37 and the lower abutment 78. Compression of the packing structure 38 will effect expansion of the elements 39 into sealing engagement with the casing wall.

Downward movement of the body member 10 relative to the expander assembly 62 during compression of the packing structure 38 causes the floating piston 67 to be moved along the expander sleeve 65, compressing the coil spring 69. Inasmuch as the chamber space 52 is still vented to the well bore at this point, such piston movement will draw well bore fluids into the chamber space 52 to completely fill it. As the body member 10 moves downwardly relative to the cage member 80, the upper body threads 98 can ratchet through the upper clutch nut threads 96 which will trap the body member in the lowermost position to which it is moved to lock the compression energy in the packing structure 38.

After the bridge plug is firmly set by theapplication of pipe weight thereto, the pipe string T is elevated while applying a small amount of right-hand torque thereto to apply an upward force to the upper body section 25. The upper body section 25 will'move upwardly relative to the lower body section 26 as the lugs 32 translate from positions 2 to positions 3, thereby bringing the seal surface 54 into contact with the seal ring 47 on the extension sleeve -45 to close-off the chamber space 52 from the well bore. This cooperative relationship of parts is shown in more detail in the enlarged view FIGURE 3. The positions 3 are located underneath the space sleeve shoulders 59, so that the limit of downward movement of the upper body section 26 is now defined by the positions 3. So limited, the seal ring 47 cannot disengage from the seal surface 54. Therefore, the chamber space 52 is closed off and cannot be vented to the well bore without appropriate manipulation of the upper body section 25 as will be described hereafter.

At the point where the chamber space 52 is initially closed, it will be appreciated that the fluids therein, as well as the fluid surrounding the tool both above and below, will have a pressure equal to the hydrostatic pressure in the well bore at the level where the tool is set. However, once the chamber 52 is closed off by the seal ring 47, upward force on the upper body section 25, occasioned by pipe strain or by pressure from below, will tend to cause upward movement of the body section 25, which movement will be accompanied by an increase in volume of the closed chamber 52 and a consequent reduction in pressure therein to values below the hydrostatic pressures outside the chamber. In either case, since the upper surfaces of the piston member 66 are exposed to fluid pressure below the packing structure 38, and the increased volume of the closed chamber 52 effects a reduction in the pressure which is acting on the lower surface 70 of the piston member 66, a pressure-differential will be developed across the efiective area A of the piston member 66 which applies downward force on the expander cone 63 to set the slips 84 tighter. As previously mentioned, upward movement of the body section 25 relative to the lower body section 26 can be effected in response to a mechanical pull on the upper section 25, or to greater pressure in the Well bore below the tool. If it is desired to initially set the slips with the maximum force to which they may subsequently be subjected to in response to greater pressure from below, this can be accomplished by simply exerting an upward strain on the pipe string T before releasing the running tool R. An upward strain suflicient to reduce the pressures in the chamber 52 to approximately atmospheric pressure will develop the maximum setting force on the slip segments 84 which can be applied in response to greater pressure from below.

In any event, once the plug has been set, the running tool can be manipulated and released from the connector head 13. Upward movement of the running tool will automatically move the sleeve valve 18 to its upper, port closing position with the spring fingers 19 engaging the shoulder 21 on the body member 10. The cross-sectional areas encompassed by the seal elements 16 and 17 can be made to be substantially the same so that the sleeve valve 18 is pressure balanced and will remain closed regardless of the magnitude of pressure above or below the tool.

The tubing string T is then lifted at the surface to position the upper packer P-1 at the upper end of the zone Z and the upper packer is set. If a cement squeeze or other pressure operation is conducted in the zone between the packers, pressure above the lower packer is greater and the net force on the expander cone 63 is directed downwardly in a typical manner. The greater pressure from above will tend to move the body section 25 downwardly, however such downward movement is limited by the spaced shoulder 59. The slip segments 84 will grip the well casing to prevent downward movement. Moreover, if the pressures in the zone Z are reduced to values below initial hydrostatic pressure by swab testing or the like, the greater pressure below the lower packer acts upwardly on the effective area B (FIGURE 5) of the upper body section 25, tending to move the body section upwardly. Such movement will effect a reduction in pressure in the chamber 52 as previously described, resulting in the application of downward force on the expander cone 63 to hold the slips 84 in gripping positions against the casing. More specifically, since the valve sleeve 18 is in the position closing 01f the bypass ports 15, the greater pressures from below act in the bore 11 on the internal surfaces of the upper body section 25 and the connector head 13 which are exposed to these pressures, while the lesser pressures in the well bore above the plug are acting on the external surfaces of the connector head 13 and the body section 25. The unbalanced transverse area of these members can be shown to be equal to the area B in FIGURE 5, which is the cross-sectional area encompassed by the seal ring 34. The difference in pressure acting over the area B will develop upward force on the connector head 13 and body section 25 which causes upward movement of same and effects a reduction in pressure in the chamber 52. The reduction in pressure in the chamber 52 develops downward force on the expander assembly 62 and increases the outward pressure being exerted by the expander cone 63 on the slip segments 84. Accordingly, the plug will not move upwardly in the casing in response to greater pressures acting from below.

When it is desired to either retrieve the tools or to move to another setting location, the upper packer P-l is released and the tubing string T is lowered to engage the running tool R with the connector head 13. The sleeve valve 18 is automatically pushed to its lower position where the bypass ports 15 are open to equalized fluid pressures across the packing structure 38. The upper body section 25 is then torqued to the left and pipe weight applied to clear the lugs 32 from the shoulder 59 and permit the seal 47 to disengage from the seal surface 54, thereby opening the chamber space 52 to the well bore. The lugs 32 will return to the positions 1 between the shoulders 55 and 56. To release the slips 84 and the packing 38, the body member 10 is rotated by the pipe string T several turns to the right to release the upper clutch nut threads 96 from engagement with the body threads 98. Then the body member is pulled upwardly to relieve the compression on the packing structure 38 so that the rings 39 will inherently retract. The splines 76 on the compression sleeve 36 will engage the flange to pull the expander cone 63 from behind the slip segments 84, thereby permitting their retraction. As the body member 10 reaches the upper limit of its travel relative to the cage member 80, the lower body threads 99 will ratchet into the lower clutch nut threads 97 to lock the cage member against movement relative to the body member 10. The lower packer is then free to be moved longitudinally in the well bore in either direction.

A new and improved well packer has been disclosed which can be anchored against movement in either direction in a well bore. The packer includes a hydraulic structure for applying a holding force to the slips in response to greater fluid pressure in the well bore below the packer, and the hydraulic structure is completely isolated from communication with fluids in the well bore above the packer while the tool is set.

Since certain changes and modifications may be made in the present invention by those skilled in the art without departing from the invention concepts involved, it is the aim of the appended claims to cover all changes and modifications falling within the true spirit and scope of the present invention.

What is claimed is:

1. A well packer for use in a well bore, comprising: a body member; expansible packing means carried by said body member and adapted to be expanded into sealing engagement with a well bore wall; slip and expander means for preventing movement in a well bore; means providing an upwardly facing surface on said expander means subject to fluid pressure below said packing means; enclosed chamber means defined in part by a downwardly facing surface on said expander means which is subject to fluid pressure in said chamber means; and hydraulic means subject to fluid pressure above and below said packing means for reducing the pressure in said chamber means in response to greater fluid pressure in the well bore below the well packer.

2. The well packer of claim 1 wherein said hydraulic means includes a piston member having a sleeve portion forming a movable wall of said chamber means.

3. The well packer of claim 1 wherein said body member includes telescopically disposed portions, said hydraulic means being constituted by one of said portions.

4. A well packer comprising: a body member; packing means carried by said body member for sealing off a well bore; slip and expander means for anchoring against movement in a well bore; an upwardly facing surface on said expander means subject to fluid pressure in the Well bore below said packing means; enclosed chamber means defined in part by a downwardly facing surface on said expander means; and hydraulic means responsive to greater fluid pressure in the well bore below the well packer for increasing the volume of said enclosed chamber to effect a reduction in fluid pressure acting on said downwardly facing surface.

5. A well packer comprising: a body member; packing means surrounding said body member and engageaible with a well conduit wall to prevent fluid flow in either longitudinal direction; normally retracted slip means; expander means for shifting said slip means outwardly into positions of gripping engagement with a well conduit wall, said expander means shifting said slip means upon movement ofsaid body member between longitudinally spaced positions; means for releasably locking said body member in one of said positions with said slip means in gripping positions; said expander means including piston means having upper and lower surfaces subject to fluid pressure respectively below and above said packing means; passage means for communicating said lower surface with the well bore above said packing means when said body member is in the other of said positions; means responsive to movement of said body member to said one position for closing said passage means to form an enclosed chamber defined in part by said lower surface; and hydraulic means on said body member for reducing the pressure in said chamber means in response to greater fluid pressure in the well bore below said packing means.

6. A well packer comprising: a body member carrying packing means for packing off a well bore; expander means and normally retracted slip means below said packing means, said slip means being shiftable to expanded position by downward movement of said expander means relative to said slip means; releasable clutch means for locking said slip means in expanded position; said expander means having an upper surface subject to fluid pressure in the well bore below said packing means; a closed, fluid-filled chamber means in said body member having a wall formed by a lower surface on said expander means; and piston means movable relative to said body member having a surface forming a movable wall of said chamber means whereby movement of said movable wall will increase the volume of said chamber means and reduce the fluid pressure therein, thereby reducing the pressure acting on said lower face of said expander means.

7. The well packer of claim 6 further including valve means for opening said chamber means to the well bore during longitudinal movement of said Well packer in a well bore.

8. The well packer of claim 6 further including a flow passage through said body member for bypassing well fluids; and valve means for opening and closing said flow passage.

9. A well packer comprising: a body member; a sleeve surrounding said body member and laterally spaced from said body member to provide a chamber space therebetween; packing means mounted on said sleeve and engageable with a well bore wall to prevent fluid flow; expander means and normally retracted slip means, said expander means and slip means having coengageable inclined surfaces for shifting said slip means into anchoring engagement with a well conduit wall; an upper surface on said expander means exposed to fluid pressure in the well bore below said packing means; a lower surface on said expander means exposed to fluid pressure in said chamber space; and hydraulic means responsive to greater fluid pressure in the well bore below said packing means for reducing the pressure in said chamber means thereby enabling said greater pressure acting on said upper surface to apply downward force on said expander means.

10. A retrievable bridge plug apparatus for use in packing off a well bore, comprising: a body member having a fluid passage valve means for opening and closing said fluid passage; packing means carried by said body member and adapted to seal against a well bore wall; normally retracted slip means adapted to be expanded into gripping engagement with a Well bore wall; expander means movable downwardly relative to said slip means for expanding said slip means outwardly; re leasable means for retaining said slip means in both retracted and expanded position; a piston member coupled to said expander means and having an upwardly facingpressure surface subject to fluid pressure in the well bore below said packing means; an enclosed chamber formed in part by a downwardly facing pressure surface on said piston member; and hydraulic means responsive to greater fluid pressure in the well bore below said packing means than above said packing means for reducing the pressure in said chamber, so that a pressure difference between the fluid pressures acting on the pressure surfaces of said piston member can force said expander means downwardly to retain said slip means in gripping engagement with awell bore wall.

11. The apparatus of claim 12 wherein said piston structure has a portion forming a movable wall of said chamber.

12.' The apparatus of claim 10 wherein said hydraulic means includes a piston structure on said body member and movable relative to said body member, said piston structure having a downwardly facing pressure surface subject to fluid pressure in the well bore below said packing means and an upwardly facing pressure surface subject to fluid pressure in the well =bore above said packing means.

13. The apparatus of claim 10 further including: valve means for opening said chamber to the well bore during running and retrieving of the bridge plug, and for closing off said chamber when the bridge plug is set in a well bore.

14. The apparatus of claim 10 wherein said piston structure has a portion forming a movable wall of said chamber, said valve means including a vlave element selectively engageable with said movable wall portion.

15. The apparatus of claim 14 further including: first releasable means for preventing engagement of said valve element with said movable wall portion during running and retrieving of the bridge plug; and second releasable means for locking said valve element in engagement with said movable wall portion when the bridge plug is set in a well bore.

References Cited UNITED STATES PATENTS 3,233,675 2/1966 Tamplen et a1. 166-120 3,361,207 1/ 1968 Chenoweth 166-120 3,399,729 9/1968 McGill 166-120 3,412,801 11/1968 Young 166-120 3,412,802 11/1968 Kisling 166-120 3,426,846 2/1969 Young 166-120 3,437,136 4/1969 Young 166-120 DAVID H. BROWN, Primary Examiner US. Cl. X.R. 166-134, 

